In addition to everything above, build an 'Ultra Transport' with 3 Advanced Troop Mods and as many Hyperwarp III engines as possible. Send it off to the side along with a fighter fleet, then blast away their home planet defenses and take over the planet in one turn. Buy an Industrial Sector (if it doesn't have one already) and then a starbase (again, only if it doesn't already have one) and queue up a ton of other Industrial Sectors. Then churn out fighters and repeat.
Take your planets that are most defended and farther away from the front-line conflict and turn them into pure economic sectors. Build up a massive tax base so you can buy capital ships by the dozen. If you have trade routes, Privateers is a must.
I think the missle-class weapons have the best space-damage ratio. Or maybe it was the best cost-damage ratio. Experiment with different types and use whatever type they aren't defending against.
Build 'Ultra Constructors', with a construction module and a bunch of Hyperwarp III engines. Keep them in reserve until you have a couple dozen of them, then send them all to one point and build a maxed-out starbase (if you can build multiple Military Starbases in such a way that the effects overlap, do that, too!). Its pretty much just a war of attrition, but since you and your allies have pretty much the same technology (or near enough), a far larger military, a far larger industrial and tax base, and the 'power of teamwork', victory should be inevitable. If you have extra resources, give them to your allies.
Then again, if you are a control freak, you could just take over (militarily or culturally) all of your allies and then crush the Dreadlords with 95% of the galaxy at your back